Technologies such as microelectronics, micromechanics and biotechnology have created a high demand for structuring and probing specimens within the nanometer scale. Micrometer and nanometer scale process control, inspection or structuring, is often done with charged particle beams. Probing or structuring is often performed with charged particle beams which are generated and focused in charged particle beam devices. Examples of charged particle beam devices are electron microscopes, electron beam pattern generators, ion microscopes as well as ion beam pattern generators. Charged particle beams, in particular ion beams, offer superior spatial resolution compared to photon beams, due to their short wavelengths at comparable particle energy.
Miniaturization is a desirable aim in semiconductor industry but also in other areas containing micrometer and nanometer components like magnetic heads and optical storage devices. These miniaturized components require process control equipment with increasing accuracy and precision. The process control includes critical dimension (CD) measurement as well as defect inspection review (DR). By using these control options, controlling of the quality and the defects of the specimen becomes possible. State of the art tools for such purposes are scanning electron microscopes (SEM) based electron beam tools.
The performance of SEM tools having beam energies of typically 100 eV to 5 keV is principally limited by the achievable spot size. The diameter of the spot is in the range of a few nanometers. This size is the result of a compromise between diffraction and chromatic aberration of the electron optical column involved.
Focused ion beam devices have been suggested, e.g., for CD and DR applications. In particular gas field ion sources (GFIS) have been proposed providing high current sub-nanometer probe sizes.
To generate a particle beam, a voltage is supplied to an emitter in the presence of an operation gas. Therefore, particles like ions of the operation gas are emitted from an emitter tip. Accordingly, as the demand for measurement tools with high resolution increases, it is desirable to decrease the spot size of the particle beam.
Further, the use of helium as operation gas has been found to be beneficial due to the short wavelength and the low mass of the ions that avoids or minimizes damage of the sample during operation. Additionally, helium ion sources have a sufficiently low energy width so that chromatic aberration will not dominate limitations to the spot size. Therefore, small spot sizes are achieved but the stability of the ion beam is still a problem. It is desirable to improve the stability of the ion beam and to assure the quality of the inspection or process operation.